A portion of the disclosure of this patent document contains command formats and other computer language listings, all of which are subject to copyright protection. The copyright owner, EMC Corporation, has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
The invention relates generally to management of multiple volumes of data distributed throughout a data storage environment, and more particularly to a system and method for management of device identifiers that are written as data and then may be physically distributed over more than one device.
As is known in the art, computer systems generally include a central processing unit (CPU), a memory subsystem, and a data storage subsystem. According to a network or enterprise model of the computer system, the data storage system associated with or in addition to a local computer system, may include a large number of independent storage devices, typically disks housed in a single enclosure or cabinet. This array of storage devices is typically connected to several computers or host processors over a network or via dedicated cabling. Such a model allows for the centralization of data that is available to many users but creates a critical hub for operations.
Recently, disk redundancy has evolved as an alternative or complement to historical backups of the information stored on this critical hub. Generally speaking, in a redundant system having at least two storage devices, such as disk storage devices, data is copied and stored in more than one place. This allows the data to be recovered if one storage device becomes disabled. In a basic approach, a first disk storage device stores the data and a second disk storage device stores a mirror image of that data. Whenever a data transfer is made to the first disk storage device, the data is also transferred to the second disk storage device. Typically, separate controllers and paths interconnect the two disk storage devices to the remainder of the computer system.
While mirror copying has important advantages, it may lead to problems in certain circumstances when all of data including some that is unique to the physical storage device itself is replicated. For instance, a manufacturer of a storage device, such as a disk drive, usually identifies it with a unique number, known as a serial number. This serial number is integrated into the device itself, typically in a fashion so it can be communicated electronically. It is known that a typical host computer system may use those serial numbers for keeping track of storage devices and may write each device""s serial number as data on the device itself. But when such data is replicated to another device, the serial number written as data will not match with the serial number integrated with the device that is receiving the replicated data. On the one hand there is the serial number integrated with the device and on the other hand there is the serial number previously written as data by a host. If the host is programmed to check for a match between these numbers then it will flag an error when they do not. In the situation where the data has been replicated from one device to another there will not be a match and the host will flag an error, possibly even prevent operation from continuing in certain circumstances.
What is needed is a way to prevent such errors occurring at a host interacting with a data storage system in which data is distributed over one or more disks but while still allowing mirror copying to occur.
The present invention is a system and method for management of device identification that is treated as device data, when such data is replicated from one storage device to at least one other storage device.
In one aspect of the invention, without reconfiguring the host""s operating software, the system employs a method to respond to and satisfy a host inquiry for the storage device""s identification information by selectively employing a special data structure. The invention is configured to create and store, in a first predetermined area, the special data structure containing a data storage device""s identification information for a storage device that will be replicated. Upon such copying, the special data is stored in another predetermined location on the device receiving the copied data.
In a similar aspect of the invention, the data structure is placed in a predetermined area, e.g. as an area reserved for use by a customer engineer and restricted from access for user data, on the device which has its data copied (the source, primary or standard device). The data structure is copied to the same area on another device (remote, secondary or target), or other device. When the host, which is preferably an AS/400 from IBM, issues an inquiry to discover the serial number of the device to which the data has been copied, the serial number is read from the data structure rather than obtained in a conventional manner from the device itself. In this way the serial number obtained and presented to the host belongs to the device which had its data copied. By implementing the present invention, the serial number moves with the data to prevent the host flagging errors as described above.